New Zealand red-crowned parakeet

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We have a red-crowned parakeet (goat parakeet) and my problem is that he is very wild. He was 4 years old when a friend of us gave him to us and it was almost 2 years ago. 2 years was not enough to tame him. He is not the first parrot we have so I just don't know what can be the problem. Is this species wilder than others? Is there any trick to tame them? Can You help me please?